This invention relates to metallic materials of improved environmental resistance particularly at elevated temperatures, and, more particularly, to such materials in the form of a metallic coating applied to a metal article for high temperature application.
Designers of power generation apparatus, such as the gas turbine engine, are interested in improving the temperature capability of high temperature operating components. Although modern alloys have mechanical properties which can withstand the force conditions experienced in such application, some have surface stability in respect to oxidation or hot corrosion resistance less than that which is desirable.
A major effort associated with the development of gas turbine engines is the effort to develop improved high temperature coating alloys and coated articles. Thus, there has been reported a variety of coatings, coated articles and coating methods for such application. One reported example of a pack diffusion process, and alloy useful in such a process, is represented by U.S. Pat. No. 3,667,985----Levine et al, issued June 6, 1972. The vapor deposition of high temperature coatings, including aluminum as an important ingredient, is shown in one form in U.S. Pat. No. 3,528,861--Elam et al issued Sept. 15, 1970. Associated with such methods has been the invention of the above-identified copending application Ser. No. 521,860 for an improved coating and article having improved resistance to high temperature environmental conditions through incorporation of the element Hf in a defined range. Such patents as U.S. Pat. No. 3,494,748-Todd; U.S. Pat. No. 3,677,789--Bungardt et al and U.S. Pat. No. 3,819,338--Bungardt et al disclose the inclusion of platinum alone or with certain other elements for improved oxidation resistance. The disclosures of each of these patents and the application are incorporated herein by reference.